An ionic liquid is a class of salt comprising a cation and an anion that is in liquid at a temperature of 100° C. or less and commonly have melting points below room temperature. While not wishing to be bound by theory, ionic liquids generally have much lower symmetry than conventional salts and the charge of cation and anion is distributed over a larger volume of the molecule by resonance in ionic liquids which is thought to contribute to their liquid state at much lower temperatures than conventional salts (e.g. NaCl, mp 801° C.). Ionic liquids are often composed of a cation comprising a heterocyclic ring and a counter anion, often inorganic in nature. The nature of the cation and anion will determine the hydrophobicity, viscosity, density and other physical parameters and properties of the ionic liquid.
Ionic liquids have been evaluated as environmentally-friendly or ‘green’ alternatives to conventional organic solvents for a wide range of organic synthetic applications. Ionic liquids have unique characteristics that distinguish them from conventional organic solvents. For example, ionic liquids are non-volatile (i.e. they do not evaporate readily into the atmosphere), they have a high polarity and charge density, they may be hydrophobic or hydrophilic, and they have unique solvating properties. As such, ionic liquids are known to be used in cleaning compositions (for example, as disclosed in US 2006/0090777 A1 and U.S. Pat. No. 7,939,485 B2). A range of ionic liquids are commercially available, or they may be readily synthesized by simple ion-exchange reactions.
It is seen as being desirable by consumers to possess white teeth. Over time, teeth can darken or become stained. Teeth naturally become more yellow with age and can also be stained by food and drink. For example, teeth can be stained by tea, coffee, red wine and tobacco. Certain antibiotics, including for example tetracycline, can also stain teeth. Many consumers wish to whiten teeth to restore the natural colour and in some circumstances wish to whiten teeth beyond their natural colour.
It is known to use peroxide-based chemicals to whiten teeth. Carbamide peroxide can be used to bleach teeth. Carbamide peroxide generates hydrogen peroxide upon contact with water and the peroxide oxidizing agent bleaches stains. Whitening can be carried out by a dental professional, by a non-dental professional such as a beauty therapist or alternatively at home by the consumer themselves. Professional tooth whitening is expensive and time consuming.
However, peroxide compounds are highly reactive, and consequently difficult to formulate. Moreover, hydrogen peroxide can spontaneously decompose to form oxygen gas (O2) and water, so that on storage, the dentifrice containers may bloat, burst or leak, and the remaining formulation will not have enough peroxide remaining to clean and whiten teeth effectively. Some initially comprise very high levels of peroxide, which decomposes over time, so that the exact amount of peroxide delivered on application is variable and largely depends on how long and under what conditions the dentifrice has been stored.
Teeth can also be whitened and stains removed using abrasive agents to physically remove stains from the teeth. Abrasive agents can include baking soda (sodium bicarbonate), silica, aluminium oxide, calcium carbonate and calcium phosphate. However, abrasive agents can cause damage to the tooth enamel and can be especially damaging to softened tooth enamel that has become soft with age or with repeated attack with oral acids or the use of acidic foods and beverages. Furthermore, abrasive agents are not always suitable for whitening the teeth of those consumers who have dentures, crowns or who wear orthodontics. For these consumers, abrasive whitening agents can damage the ceramic surfaces or may not provide effective reach to clean between orthodontic wiring.
A biofilm is a structured group of microorganisms encapsulated within a self-developed polymeric extracellular matrix. Biofilms are typically adhered to a living or inert surface. In the human or animal body biofilms can form on any internal or external surface. Biofilms have been found to be involved in a wide variety of microbial infections in the body and cause a number of conditions including urinary tract infections, middle-ear infections, and in particular, diseases of the oral cavity.
Dental plaque is formed from a biofilm precursor, and is present to some degree on virtually all dental surfaces. It comprises a dense microbial layer consisting of a mass of microorganisms embedded in a polysaccharide matrix. Plaque may form on any part of the tooth surface, and is found particularly at the gingival margin, and in cracks in the enamel. The danger associated with the formation of plaque on the teeth lies in the tendency of plaque to build up and eventually produce gingivitis, periodontitis and other types of periodontal disease, as well as dental caries and dental calculus.
Plaque itself adheres very firmly to dental surfaces and rapidly reforms on the tooth surface after it is removed. Current plaque removal methods rely primarily on the mechanical removal of plaque. These methods, which include brushing, brushing with an abrasive toothpaste, flossing, using interdental cleaners, scraping, using sonic energy (e.g. Sonicare toothbrushes) and ultrasound (e.g. Ultreo toothbrushes), in part, rely on a good brushing or flossing technique which may consumers simply do not possess. Moreover, these methods are particularly inefficient in removing stubborn plaque, or plaque hidden deep within cavities and fissures of teeth, or within gum pockets.
It is also known in the art to incorporate antimicrobial agents in oral compositions which destroy or retard the growth of bacteria. However, bacteria present in a biofilm or plaque deposit exhibit increased resistance to antimicrobial agents because the dense extracellular matrix and the outer layer of cells protect the bacteria found in the interior of the deposit from the effects of the antimicrobial agents.
It would be desirable to provide improved methods and compositions for whitening teeth that can achieve whitening benefits without damaging tooth enamel. It would also be desirable to provide improved methods and compositions for whitening the teeth of consumers who possess dentures, crowns or who wear orthodontics.